Wire harnesses each consisting of a plurality of bundled wires are widely used for internal wiring in a building and for connection between vehicle devices. In routing a wire harness in a vehicle by having the wire harness penetrate a through-hole formed on a vehicle body panel and the like, such a configuration considering protection and water-proof of the wire harness is known that fits the fitting portion of a grommet with the through-hole and has the wire harness inserted inside a cylindrical portion integrally connected with the fitting portion. For example, Patent Literature 1 describes a method of fitting the fitting portion of a grommet with a through-hole by having a worker pull the cylindrical portion of the grommet, the fitting portion of which is disposed behind the through-hole with respect to the worker, toward the worker side.